Degree Name

Master of Science

Department or Program



Michael, Olson, W


Prolonged loading of the anterior cruciate ligament (ACL) influences thigh muscle activity during walking. The resulting neuromuscular responses of the thigh musculature and ground reaction forces (GRF) during gait initiation after ACL loading are determined.

PURPOSE: To observe electromyography (EMG) activity of thigh muscles and GRF during gait initiation before and after static loading of the ACL.

METHODS: Eleven healthy individuals (5 male, 6 female; aged 21.6 ± 2.9 years, height 1.69 ± 0.10 m, mass 69.5 ± 12.3 kg) with no history of lower extremity pain/injury participated. Participants were seated while the left knee was flexed to 90º and secured to prevent movement. Maximal voluntary isometric contractions were performed in knee flexion and extension. A padded cuff was then fitted around the proximal lower leg, and a cable was fixed around the pad. The cable ran through a pulley system and loaded the leg for 10 min with a 200 N load for males and 150 N load for females respectively. Gait was initiated with the left leg five times immediately before and after static loading. EMG of rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF), and semimembranosis (SM) were collected. GRFs were normalized to body weight of the individual and analyzed during the first step. One way analysis of variance (ANOVA) was used to identify changes between pre and post-loading steps during the first 50% of the stance phase. Alpha was set at < 0.05.

RESULTS: Average EMG of RF was increased (p< 0.05) but did not change significantly in VL, VM, BF and SM muscles from pre to post walking trials. Peak Fy and Fz were not statistically significant (p > 0.05) during the post-walking trials. Peak timing of each muscle during heel contact did not vary significantly after loading the knee joint. No significant difference was found in average Fx, Fy and Fz forces during the post-walking trials. Rate of force development changed, but not uniformly between the participants and the change was not statistically significant (p > 0.05).

CONCLUSION: The results of the study conclude that there is a change in the thigh muscle activity from pre to post walking trials after loading the knee joint. Statistically significant change was seen in RF muscle. GRF did not show any significant difference between the trials. Thus the induced ACL creep influences the thigh muscle activity in walking, and active individuals should try to avoid ligamentous creep and include frequent rest periods in order to have a higher level of performance, as well as reduce the risk of injury.